Process of prehardening austenitic manganese steel



Aug. 7, 1962 H. c. DOEPKEN 3,048,505

PROCESS OF PREHARDENING AUSTENITIC MANGANESE STEEL Filed Aug. 12, 1959 AUSTENITIC MANGANES E STEE L FIRST-H EATING ZONE COOLING ZONE SECOND- HEATING ZONE QUENCHING ZONE PREHARDENED AUSTENITIC MANGANESE STEEL IN V EN TOR. HERBERT C. DOEPKEN ATTORNEY 3,048,505 Patented Aug. 7, 1962 has .HENING AUSTENITIC MANGANESE STEEL Herbert C. Doeplten, Narberth, Pa., assignor to Manganese Steel Forge Company, a corporation of Pennsylvania Filed Aug. 12, 1959, Ser. No. 833,344

12 Claims. (Cl. 148-137) Carbon 1.00% to 1.40%. Manganese 10.00% to 14.00%. Phosphorus 0.10% max. Sulphur 0.01% to 0.03%. Silicon 0.10% to 0.30%.

In the use of the Hadfield composition, it is convention al practice to vary this composition somewhat, as by varying the proportions given in his formula (for example, the carbon may be in the range of 0.65% to 1.40%, or the silicon may be 2.00%), or by adding supplementary ingredients such as nickel, chromium, vanadium, or molybdenum. But regardless of such changes, the steel does not lose its identity as Hadfield-type-steel which is austenitic and non-magnetic, and the problem of hardening is still present in all these forms regardless of whether the material is cast or wrought.

Such a manganese steel composition isnorrnally heattreated by raising the temperature above the upper critical point until it becomes completely austenic and then quenching it in water. This temperature varies from 1800 to 1900 F. After this heat treatment, the material remains essentially austenitic. In this condition the material has approximately a yield strength of 55,000 to 75,000 p.s.i., an ultimate strength of 135,000 to 165,000 p.s.i., and an elongation of 35% to 60%. Such austenitic steel is inherently ductile to a high degree but lacks desired hardness since its hardness is usually only 180 to 215 Brinell.

The usual manner in which austenitic manganese steel attains its long-wearing characteristics is by work-hardening in use. Impact on manganese steel increases the surface hardness to about 450 to 600 Brinell, depending on the severity of the impact. The depth of work-hardening also increases wtih increasing severity of impact. For a great number of heavy duty operations, this work-hardened material is compl tely satisfactory and outwears any other material.

There are, however, a large number of applications wherein the severity of impact is not sufiiciently great to cause immediate work-hardening. Consequently, there is substantial wear before a work-hardened surface is developed, or the part wears out without developing a substantial work-hardened surface.

Accordingly, it has been a problem to increase the initial hardness of the material before it is put into service, so that the opportunity for abrasive wear to occur before work-hardening developed would be minimized. There has been substantial work done to accomplish this result by utilizing shot peening, cold rolling, or by otherwise cold-working the material. However, prehardening by cold-working before use is generally unsatisfactory for many reasons, including lack of control of the degree and of the uniformity of the hardness produced, as well as the relatively high cost involved in such operations.

It is an object of this invention to overcome the aforementioned diificulties and problems.

It is another object of this invention to provide a process of prehardening austenitic manganese steel before use to form a steel which is of desired hardness without being brittle.

It is another object of this invention to provide a process which is controllable so as to vary the degree of hardening and the degree of retained ductility of the steel.

It is another object of this invention to provide a process which uniformly produces an austenitic manganese steel product of predetermined uniform hardness.

It is a further object of this invention to provide a proces which produces prehardened austenitic manganese steel which may be welded.

Other objects and advantages of this invention, including its simplicity and economy, as well as the ease with which it may be adapted to existing equipment, will further become apparent hereinafter, and in the drawing which shows diagrammatically the various zones through which the steel is conveyed in accordance with the process of this invention.

Although specific terms are used in the following decription for clarity, these terms are not intended to define or limit the scope of the invention.

The present invention starts with austenite (which is inherently ductile but lacks desired hardness) and modifies it in essential particulars, first, by prehardening it (with accompanying loss of ductility) and then by reclaiming apart only of the original ductility without sub Turning now to the drawing, there is shown a firstheating zone 1, a cooiing zone .2, a second-heating zone 3, and a quenching zoned.

According to the present invention, fully. austenitic 10.00% to 14.00% manganese steel is delivered to the first-heating zone 1, and there uniformly heated at a carefully-controlled predetermined degree of temperature, which i uniformly maintained, for a suflicient length of time to develop an acicular structure having carbide needles within the grains of the steel but with the boundaries of the grains being comparatively free of carbide precipitation.

The steel is then delivered to cooling zone 2 where it is slowly cooled to ambient temperature.

. After the steel has been cooled, it is delivered to secend-heating zone 3 where it is subjected to a temperature below the transformation'point at which the steel would change completely into austenite. It is subjected to this temperature, which is uniformly maintained, for a sutlicient length of time to diminish the size and round an the sharp points of the needles through a partial solution only of the previously precipitated carbides. After first-heating zone 1 uniformly to this temperature for about six hours.

In cooling zone 2, the steel is slowly cooled to ambient temperature. Satisfactory. results have been obtained when the cooling has lasted for a period of time between 10 to 48 hours.

zone 4- for immediate quenching in water.

uniformly for two hours.

In second-heating zone 3, the steel is heated to a temperature in the range of 1350 F. to 1500 F. to a prepartially dissolved to the extent of removing their sharppoints and making the needles smaller and of approximately the shape of little round balls. These balls are just as hard as the needles, but because the balls are surrounded by ductile material, and because the sharp points of the needles have been eliminated, the steel has regained adequate ductility, that is, a part only of its original ductility sufficient to resist heavy impact in use. This is effected without substantial loss of the hardness imparted to the steel in the first-heating step.

The steel is subjected to the heat of the second-heating zone 3, which is maintained uniformly, for a period of time of not less than two hours, after which the steel is quickly quenched. This quenching is preferably accornplished by immersing the steel in water.

The Brinell hardness of the resulting product may be controlled by controlling the temperature of the second- I heating zone 3. For example, it has been found that subjecting the steel in the second-heating zone 3 to a temperature of 15 F. gives the resulting product a hardness of 300 Brinell, subjecting the steel in second-heating zone 3 to a temperature of 1450 F. gives a hardness of 350 delivered to cooling zone 2 where it is slowly cooled for a period of ten hours to ambient temperature.

Next, the plate is delivered to second-heating zone 3 wherein it is subjected to a predetermined uniform temperature of substantially 1400 F. which is maintained uniformly'for two hours. quenched by transferring it to quenching zone 4 and submerging it in water. The resulting hardness of the plate was found to be 400 Brinell.

It is to be noted in all of the above examples that the fully austenitic rolled steel is heated to a temperature of 1200 P. which is maintained uniformly in first-heating zone It for a sufiicient length of time to develop an acicular structure having precipitated carbide needles within the grains of the steel. This structure forms uniformly within the grains, with some carbide precipitation forming on the grain boundaries but not in unwanted concentrations.

Brinell, and subjecting the steel in second-heating zone 3 V to a temperature of 1400 gives a hardness of 400 Brinell.

' Example 1 A rolled-steel plate, such as is used by many asphalt plants for asphalt mixer liners, formed of fully austenitic 10.00% to 14.00% manganese steelis subjected to the process of this invention. This plate is delivered to firstheating zone 1, and is subjected to a predetermined tem perature of substantially 1200 F. which is maintained uniformly for about 'six hours. After this, the rolledsteel plate is delivered to the coolingzone 2 where it is cooled slowly to ambient temperature for a period of ten hours.

Then the steel plate is delivered to second-heating zone 3 where it is heated'to a predetermined temperature of substantially 1450 P. which is maintained uniformly for two hours. Next, the steel is delivered to quenching The processed plate was found to have a hardness of 350 Brinell.

Example 2 V A rolled-steel plate, such as is used by the automobile industry for shot blast liners, formed of fully austenitic 10.00% to 14.00% manganese steel, is subjected to the process of this invention. The plate is delivered to firstheating zone 1 wherein it is subjected to a predetermined uniform temperature of substantially 1200 P. which is maintained uniformly for about six hours. Then the plate is delivered to cooling zone 2. where itis slowly cooled for ten hours to ambient temperature.

Then the steel plate is delivered to heating zone 3 wherein it is subjected to a predetermined uniform temperature of substantially 1500 P. which is maintained Next, it is immediately quenched by being delivered to quenching zone 4- and submerged in water. The resulting hardness of the plate was found to be 300 Brinell.

' for blast furnace bell liners, is formed of fully austenitic 10.00% to 14.00% manganese steel. The plate is subjected to the process of this invention by delivering it to heating zone Lwhere it is subjected to a predetermined uniform temperature of approximately 1200 P. which is maintained uniformly for siX hours. Then the plate is temperature range of such first heat.

Optimum precipitation of the needles of the acicular structure was obtained when the steel had been uniformly heated to 1200 F. which was maintained uniformly for a period of sixhours. This acicular structure of the steel renders it very brittle although it has the quality of high hardness. But because of the brittle characteristic, the steel has no commercial value.

To eliminate unwanted brittleness, the second heat treatment is then applied to the steel in second-heating zone 3. A two-hour soak at 1450 F. (as in Example 1) is foundto be satisfactory. After this soak, the material is immediately water-quenched from that temperature.

The purpose of the second heating is to partially dis solve the carbides by dissolving the sharp edges only of the acicular structure developed in the first-heating zone, thereby leaving an austenitic matrix with carbide precipitates uniformly distributed throughout the grains. These carbides are round or oblong with nosharp edges. The purpose of this second heating is not to establish an austenitic structure, nor is its purpose to dissolve carbides completely. The purpose of the second heating is only to sufliciently dissolve the sharp edges from each carbide precipitate in order to restore ductility without reducing hardness.

The ranges of temperature heretofore indicated for the first and second heats have been foundt suitable for the practice of the invention in connection with the usual Hadfield compositon of austenitic manganese steel referred to in column 1 hereof. It is to be noted that these indicated temperatures fall within the following limtis: in the first heat, above that at which ferrite goes into solution in the austenitic matrix but below the temperature at which carbide fully dissolves into the austenitic matrix, and in the second heat, higher than the temperature employed in the first heat but still within the limits of the If the usual Hadfield composition is varied somewhat in accordance with the conventional practice referred to in column 1 hereof, the ranges of temperatures employed in the first and second heats in practicing the present invention are varied withinsuch limits in order to suit the changed composition.

The steel after being subjected to the process of the present invention has the following approximate physical characteristics:

Yield strength, 120,000 to 140,000 p.s.i., Ultimate strength, 135,000 to 165,000 p.s.i., Elongation in 2 inches, 10% to 16%.

The material has a hardness which may be varied from 300 to 400 Brinell. The material may be work-hardened in use to 450 to 600 Brinell. In all cases, the desired adequate ductility is retained in the material.

Steel which has been prehardened before use by the process of the present invention has been successfully used in blast furnace bells, woven screens (of a type which requires hardness and ductility), asphalt mixer liners, shot blast liners, skip tub liners, and receiving hopper liners.

Then the plate is immediately While the hereinbefore discussed examples refer to the use of the inventive process with wrought steel, the process is equally applicable to articles of manganese steel produced by a cast process.

It is to be understood that the form of the invention herewith shown and described is to be taken as a preferred embodiment, and various changes may be made within the skill of the art Without departing from the spirit or scope of the invention, as defined in the subjoined claims.

The claimed invention:

1. A process of prehardening austenitic manganese steel to form a steel of superior hardness and ductility, comprising heating austenitic manganese steel to a temperature above that at which ferrite goes into solution in the austenitic matrix and below the temperature at which carbide fully dissolves into the austenitic matrix, in order to precipitate carbide needles within the grains of the steel, allowing the steel to cool to ambient temperature, heating the steel to a higher temperature than that in the first said heating step but within the first said heating range, in order to diminish the size and round oit the sharp points of said carbide needles, and quenching the steel.

2. A process of prehardening austenitic manganese steel to form a steel of superior hardness and ductility, comprising the steps of heating austenitic manganese steel to a temperature in the range between 1100 F. to 1300 F. to precipitate carbide needles within the steel, allowing the steel to cool to ambient temperature, heating the steel to a temperature in the range of 1350 F. to 1500 F. to diminish the size and round ofi sharp points of the carbide needles, and quenching the steel.

3. The process defined in claim 2, wherein said steel in said first-heating step is heated to a uniform temperature of approximately 1200 F., and the steel contains 1.00% to 1.40% carbon.

4. The process defined in claim 2, wherein said steel is subjected to said first-heating step for about six hours.

5. The process defined in claim 2, wherein said steel is slowly cooled for to 48 hours to ambient temperature in said cooling step between said first and second heats.

6. The process defined in claim 2, wherein said steel is subjected to said second-heating step for more than two hours.

7. The process defined in claim 2, wherein said quenching is accomplished by immersing said steel in water.

8. A process of prehardening 10.00% to 14.00% manganese steel before use to form a steel of superior hardness and ductility, comprising heating said steel at approximately 1200" F. and uniformly maintaining the temperature for about six hours to develop an acicular structure having needles within the grains but with the boundaries of the grains being comparatively free of varbide precipitation, slowly cooling said steel for 10 to 48 hours to ambient temperature, heating the steel to a temperature of about 145 0 F. and uniformly maintaining the temperature for at least two hours to diminish the size and round off sharp points of said needles, and then water-quenching said steel, whereby to form a prehardened manganese steel.

9. A process of prehardening 10.00% to 14.00% manganese steel before use to form a steel of superior hardness and ductility and a Brinell hardness of substantially 300, comprising heating said steel at approximately 1200 F. and uniformly maintaining the temperature for about six hours to develop an acicular structure having needles within the grains but with the boundaries of the grains being comparatively free of carbide precipitation, slowly cooling said steel for 10 to 48 hours to ambient temperature, heating the steel to a temperature of about 1500 F. and uniformly maintaining the temperature for at least two hours to diminish the size and round off sharp points of said needles, and then water-quenching said steel, whereby to form a prehardened manganese steel with a Brinell hardness of substantially 300.

10. A process of prehardening 10.00% to 14.00% manganese steel before use to form a steel of superior hardness and ductility and a Brinell hardness of substantially 400, comprising heating said steel at approximately 1200 F. and uniformly maintaining the temperature for about six hours to develop an acicular structure having needles within the grains but with the boundaries of the grains being comparatively free of carbide precipitation, slowly cooling said steel for 10 to 48 hours to ambient temperature, heating the steel to a temperature of substantially 1400" F. and uniformly maintaining the temperature for at least two hours to diminish the size and round ofi sharp points of said needles, and then water quenching said steel, whereby to form a prehardened manganese steel with a Brinell hardness of substantially 400.

11. A process of prehardening before use austenitic 10.00% to 14.00% manganese steel, having carbon in the range of 1.00% to 1.40%, to form a steel of superior hardness and ductility, consisting of heating said manganese steel at approximately 1200 F. and uniformly maintaining the temperature for about six hours, slowly cooling said steel for 10 to 48 hours to ambient tempera ture, heating the steel to a temperature of about 1450 F. and uniformly maintaining the temperature for at least two hours, and then water-quenching said steel, whereby to form a prehardened manganese steel.

12. P-rehardened austenitic manganese steel having a composition which includes carbon 0.65% to 1.40%, manganese 10.00% to 14.00%, phosphorus up to 0.10%, sulphur 0.01% to 0.03%, silicon 0.10% to 2.00%, said steel being non-magnetic and having an elongation in two inches of 10% to 16%, a hardness in the range of 300 to 400 Brinell, and an austenitic matrix with rounded carbide particles dispersed therethrough.

References Cited in the file of this: atent UNITED STATES PATENTS 1,427,121 Nichols Aug. 29, 1922 1,851,903 Hall Mar. 29, 1932 1,975,746 Hall Oct. 2, 1934 OTHER REFERENCES American Society for Steel Treating, volume 12, July- December 1927, page 111. 

1. A PROCESS OF PREHARDENING AUSTENITIC MANGANESE STEEL TO FORM A STEEL OF SUPERIOR HARDNESS AND DUCTILITY, COMPRISING HEATING AUSTENITIC MANGANESE STEEL TO A TEMPERATURE ABOVE THAT AT WHICH FERRITE GOES UNTO SOLUTION IN THE AUSTENITIC MATRIX AND BELOW THE TEMPERATURE AT WHICH CARBIDE FULLY DISSOLVES INTO THE AUSTENITIC MATRIX, IN ORDER TO PRECIPITATE CARBIDE NEEDLES WITHIN THE GRAINS OF THE STEEL, ALLOWING THE STEEL TO COOL TO AMBIENT TEMPERATURE, HEATING THE STEEL TO A HIGHER TEMPERATURE THAN THAT IN THE IN ORDER TO DIMINISH THE SIZE AND ROUND OFF THE SHARP POINTS OF SAID CARBIDE NEEDLES, AND QUENCHING THE STEEL. 